Overview of shortness of breath

Question 1

What is the partial pressure of oxygen in dry air?

Answer 1

Around 21.2 kPa at sea level

Question 2

Wwhat is hypoxaemia

Answer 2

abnormally low arterial partial pressure of oxygen (Pa02)

Question 3

What is hypoxia?

Answer 3

Hypoxia is defined as a low tissue partial pressure of oxygen either due to a reduction the supply of oxygen or the ability to use it.

Question 4

WWhat is the classic sign of hypoxaemia?

Answer 4

central cyanosis

Question 5

What is Aa difference

Answer 5

Aa difference = PA02 — PaO2

Question 6

How do you find PAO2

Answer 6

Calculated using alveolar gas equation

Question 7

How do you find PaO2

Answer 7

Measured by performing an arterial blood gas analysis

Question 8

What is Aa difference in young adults?

Answer 8

2kPa

Question 9

What is Aa difference in elderly?

Answer 9

5kPa

Question 10

What are the causes of hypoxaemia Give examples for each effect

Answer 10

High altitude e.g. climbing Everest
Hypoventilation e.g opioid overdose
Diffusion defect e.g fibrosis
VA:Q mismatch  e.g pulmonary embolism
Right-to-to left cardiac shunt e.g congenital cyanotic heart 
disease

Question 11

How does High altitude affect Aa difference

Answer 11

Normal

Question 12

How does Hypoventilation affect Aa difference

Answer 12

Normal

Question 13

How does Diffusion defect affect Aa difference

Answer 13

Increased

Question 14

How does VA:Q mismatch affect Aa difference

Answer 14

Increased

Question 15

How does Right-to-to left cardiac shunt affect Aa difference

Answer 15

Increased

Question 16

What are the causes of tissue hypoxia

Answer 16

Hypoxaemia
Stagnant hypoxia
Anaemia hypoxia
Histotoxic hypoxia

Question 17

When should you suspect hypoxia?

Answer 17

Anxiety
Euphoria
Confusion/poor judgemental/irritability
Lack of coordination
Tachypnoea, use of accessory muscles
Poor coordination
Tunnel-vision
Loss of consciousness/coma
Seizures

Question 18

Clinical features of type II respiratory failure

Answer 18

Vary according to the underlying cause
Headache (cerebral vasodilatation)
Flapping tremor of wrist
Bounding pulse

Question 19

What is the MRC Dyspnoea

Answer 19

Grade:
1 Not troubled by breathlessness except on strenuous exercise

2	Short of breath on hurrying or walking up a slight hill

 3	Walks slower than contemporaries on level ground, or has to stop for breath when walking at own 
               pace

4	Stopes for breath after about 100m or after a few minutes on level ground

5	Too breathless to leave the house, or breathless when dressing or undressing

Question 20

Why does high altitude cause hypoxaemia

Answer 20

Fall in barometric pressure
leads to a decrease in PLO2
and PAO,

Question 21

Why does hyperventilation cause hypoxaemia

Answer 21

Decreased alveolar ventilation ‘pump failure’
Leads to a decrease in PAO2
Increase Increase PACO2

Question 22

Why does diffusion defect cause hypoxaemia

Answer 22

Leads to a decrease in Pa02

Question 23

Why does VA:Q mismatch cause hypoxaemia

Answer 23

Leads to a decrease in PaO2

PACO2 low or normal

Question 24

Why does right to left cardiac shunt cause hypoxaemia

Answer 24

Shunted blood bypasses the alveoli and cannot be oxygenated resulting in a very low Pa02

Question 25

What is meant as type 2 respiratory failure

Answer 25

combination of low oxygen and high carbon dioxide

Question 26

What is meant as type 1 respiratory failure

Answer 26

combination of low oxygen and normal or low carbon dioxide

Question 27

What does hyperventilation result in?

Answer 27

type 2 respiratory failure

Question 28

What does VA:Q mismatch result in?

Answer 28

type 1 respiratory failure

Question 29

What does opioid overdose result in

Answer 29

type 2 respiratory failure

Question 30

What does pulmonary embolism result in

Answer 30

type 1 respiratory failure